Plasmonic planar antenna for wideband and efficient linear polarization conversion

In this Letter, we demonstrate both theoretically and experimentally that plasmonic planar L-shaped antenna can nearly totally convert the linear polarization of light with a high efficiency in the infrared (3-5 μm). The nanoantenna geometry is engineered so that the polarization conversion occurred on a 1 μm-wide band ([3.25-4.25] μm) with a mean polarization conversion ratio of 95%. We show that this effect is due to two localized resonances in the L-shaped antenna, which wavelengths are tunable with the in-plane geometry of the nanoantenna. Eventually, the angular independence of the polarization conversion effect is evidenced.